Processing used in image and video processing, such as scaling and de-interlacing, will bring about an aliasing effect to edges of the images, that is, in the processed image, aliasing effect or jagginess occurs near edges that look straight in the source image. In graphics rendering, when processing a straight line, aliasing will occur in the rendered straight line if mishandled. When aliasing occurs in an image, it is necessary to remove the aliasing.
A conventional anti-aliasing system is as shown in FIG. 1, in which the edge of an image is detected, then a filter is selected from a group of directional filters according to the direction of the edge to perform filtering along the direction of the edge, and finally the source image and the directional filtering result are combined by means of the confidence level of the edge to output the final result. Such an anti-aliasing system has several disadvantages. The first disadvantage is that the direction is usually quantified into a limited number of directions, each direction corresponding to a filter along the direction, thus for directions that fall between the quantified directions, only the nearest quantified direction can be selected for filtering, or the results of filtering along several neighboring quantified directions are combined, and the accuracy is affected. The second disadvantage is that, when processing a low angle (i.e. an angle close to the horizontal direction) pixel whose edge direction is lower than the lowest angle among the quantified directions, aliasing occurred in said direction cannot be effectively handled. The third disadvantage is that, when processing a low angle (i.e. an angle close to the horizontal direction) pixel, pixels used for filtering are far away from one another, so mistakes are readily occur.